In 1990's, blue LEDs were developed and marketed, and white LEDs in combination with YAG (yttrium-aluminum-garnet) fluorophor that emits yellow light at high efficiency upon reception of light from the blue LED chip were also developed. In response to this, development directed toward stabler chromaticity of white color or higher brightness has been being advanced in view of applications and progresses for general lighting using LEDs and backlight light sources of LEDs for TV use. A large challenge in making such development is to improve the thermal resistance and light resistance of the sealing resin for sealing the LED chip.
White LEDs have a problem of deterioration of peripheral members due to blue light, which is emitted from the LED chip in use and which is short in wavelength and large in energy. When epoxy resin is used as the sealing resin, there occur such deteriorations as discoloring of the sealing resin due to the short wavelength and large energy of the emission of the LED chip, so that high-brightness light emission cannot be maintained for long time. As sealing resins that can meet the desire for that long-time high-brightness light emission, silicone-based resins have been being in use.
However, silicone-based resins, although excellent in light resistance, are poor at gas barrier property in not a few cases. Poor gas barrier property of the sealing resin causes occurrence of condensations at the interface between the sealing resin and the substrate or package due to permeation of steam as an example, leading to deteriorations or short-circuits of interconnect patterns or chip electrodes. Also, while sealing resins for vehicle use need to have corrosive-gas resistance, poor gas barrier property of the sealing resin causes occurrence of deteriorations or short-circuits of the interconnect patterns or chip electrodes, as in the case of condensations, making it impossible to satisfy the reliability.
Meanwhile, some silicone-based resins are denatured with resins of good gas barrier property, but those are lowered in light resistance. Under the current circumstances, it is quite difficult to find out an optimum sealing resin.
Besides, since silicone-based resins are so weak in adhesion that heat generation of the chip or the like causes resin peeling to occur at interfaces with peripheral members due to differences in coefficient of thermal expansion. This leads to characteristic deteriorations as a light emitting device such as degradation of light-emission brightness.
Thus, as it stands, even adopting silicone-based resins can hardly meet the desires for thermal resistance, light resistance and gas barrier property.
In this connection, Patent Literature 1 (JP 2004-339450 A) discloses an LED package for improving the light resistance of the sealing resin. This LED package, including an opening portion composed of a bottom face and a side wall, is integrally formed from formation resin so that the bottom face of the opening portion has end portions of a positive external electrode and a negative external electrode exposed with specified distances, respectively. It is also described that in this LED package, a primer layer is provided on the LED package surface before providing mold resin (sealing resin). Further, in this LED package, used as the primer layer are primer compositions characterized by including acrylic polymers, silanol condensation catalysts, silane coupling agent and/or epoxy group-containing compounds as an essential component in a solution. As a result of this, peeling after the light resistance test is suppressed, and the bonding reliability between the LED package and the sealing resin is improved.
In the prior art shown above, although improvement of the adhesion property during the thermal resistance test and the light resistance test by the primer layer is fulfilled, yet improvement of the gas barrier property is not disclosed.